1. Field of the Invention
The present invention relates to a method for manufacturing ultra fine tungsten carbide-cobalt composite powder. More particularly, it relates to a method for manufacturing ultra fine tungsten carbide-cobalt composite powder by going through calcination process, reduction process, carburization process successively at a certain reaction temperature in a given each gas atmosphere, after original and efficient dry-mixing tungsten compounds with cobalt compounds.
2. Description of the Related Art
Tungsten carbide-cobalt composite powder have high hardness and excellent wear resistance, and thus is widely used for cutting tools, wear resistant tools, impact resistant tools and metal mold material, etc. Also, as the tungsten carbide (WC) particles get ultra fine, it has high hardness and wear resistant properties, and has mechanical properties of higher toughness than that of other cutting material due to a effect of Co binder phase.
According to the method for manufacturing tungsten carbide (WC) powder, which is currently being industrially mass-produced, tungsten carbide (WC) powder is manufactured by pulverizing carburization powder prepared by calcinating and reducing tungstic acid (H2WO4), ammonium para-tungstate (APT) extracted from tungsten mineral into an appropriate size by a milling process, mixing carbon powder into the carbonizing the mixture at high temperature of at least 1400. In order to make this into a commercial product, various tools including cutting tools are manufactured by mixing a metal binder, Co powder, through a wet milling process to ensure higher toughness.
However, said manufacturing method has problems that the tungsten carbide (WC) particles are coarse by being compounded at high temperature, or that the milling process is performed for a long period of time at the time of adding Co powder. Also, in this manufacturing method, since the reduction process and carburization process are performed at high temperature, it is impossible to manufacture ultra fine powder.
As attempts to improve such conventional methods, there are Korean Patent Laid-Open Nos. 1998-0083671 & 2001-0113364, which relate to mechanochemical processes. Explaining this method in more detail, after preparing a solution appropriate for the target composition by dissolving tungsten salt (AMT((NH4)6(H2W12O40).4H2O)), cobalt salt (Co(NO3)2.6H2O), and as grain-growth inhibitors, aqueous salt such as ammonium metavanadate (AMV), Cr-nitrate, Ta-chloride, which are salts of V, Cr, Ta in water, uniform precursors are manufactured by drying this at a spray dryer. Said uniform precursor manufactures a uniform tungsten-cobalt oxide by going through a salt removing process which removes the salt and water in the air, and this is reduced and carbonized to manufacture ultra fine cemented carbide composite powder. This method can manufacture ultra fine nano phase composite powder, but it has disadvantages such that the cost of the aqueous salt is relatively high, and that the processes for preparing a solution and spray drying are added.
As another method, in Korean Patent Laid-Open No. 2003-0024174, ultra fine cemented carbide powder is manufactured by performing reduction and carburization at the same time using hydrogen and expensive methane gas in a furnace after wet milling tungsten oxide (WO3) and cobalt oxide (Co3O4) by an attritor. However, this method has fundamental problems in efficiency and economical efficiency since wet milling through the attritor takes a long period of time of at least 30 hours and a drying process is added thereafter. Further, it has been known that it is impossible to manufacture 0.3 μm sized ultra fine powder with the fine grinding process. Also, there are problems in stabilizing properties and mass-producing equipments according to the regulation of carbon content of the powder quality manufactured by performing reduction and carburization at the same time by inputting hydrogen, methane, hydrogen gas successively.